Production of formation fluids, oil and gas in particular, from production wells tends to decrease over time in part due to gradual decreasing formation permeabilities in the vicinity of the production well. After a such a decrease in the formation permeability in the vicinity of the wellbore, a significant increase in the production rates can typically be realized by an acid treatment of the formation from the production well. U.S. Pat. Nos. 4,741,844, 4,919,827 and 5,039,434 each disclose such acid treatment processes. A typical problem with these acid treatment processes is that the injected acids tend to flow into the formations through zones that already have acceptable permeabilities, bypassing the more impaired zones.
U.S. Pat. No. 4,741,844 addresses this problem by providing an acidization composition and method that creates a foam, impairing permeability in highly permeable zones during the acid treatment and thereby forcing acidization solution into the more impaired zones. Acidization solutions taught in this patent include solutions containing a foam stabilizing formulation of salts of alkyl sulfonates and alkyl ether sulfates, along with a combination of an alcohol having one to five carbons and an alcohol having at least eight carbon atoms. Although compositions such as these can be effective to direct acid treatment solutions to less permeable strata, when production is resumed, surfactants such as the alkyl sulfonates tend to cause emulsions and/or foams in oil-water separators at the surface. These emulsions and foams create significant operational problems.
It is therefore an object of the present invention to provide a method to increase the permeability of a formation in the vicinity of a wellbore for producing formation fluids wherein the permeability is increased by an acidization treatment and wherein the more permeable zones of the formation can be temporally blocked by a foam, but wherein surfactants will not be present in the fluids produced after the acidization treatment in a concentration sufficient to cause foaming or formation of emulsions in surface separators.